23rd Congress of International Council of the Aeronautical Sciences, 8-13 September, 2002, Toronto, Canada
Paper ICAS 2002-R12

NUMERICAL MODEL OF SINGLE MAIN ROTOR HELICOPTER DYNAMICS

D. Cvetkovic (1), I. Kostic (1), C. Mitrovic (1), A. Bengin (1), D. Radakovic (2)
(1) Faculty of Mechanical Engineering, Yugoslavia; (2) Federal Bureau for Measures and Precious Metals, Belgrade, Yugoslavia

Keywords: fluttering, throwback, climb, equilibrium

Helicopters have six degrees of freedom, so for the simplification it is assumed that motion can be separated into longitudinal and lateral motion and that they can be investigated independently. It is noted that the mathematical model of the helicopter is regarded to helicopter forward motion at velocity W. A mathematical model that would incorporate all helicopter motion, all together with takeoff and landing, would be far complicated. Influence of resonance and vibration is also ignored. The blade through back is also ignored in this paper, because otherwise the blade angle velocity in the plane of rotation would no longer be constant. Separate study of individual motions of blades is a great simplification, because there is an interdependency of all blade motions. If the motions are not separated, then it is necessary to analyze the stability of all the motions of the blade. Determination of aerodynamic derivatives is related to series of approximations. It should be noted that, besides assumptions in modeling, also mathematical simplifications were made (for example, omittance of higher order small values in equations) which couldn’t have been derived in the form of an assumption due to their meaning which is tightly related to a specific equation. It is possible to determine projections of position vector with respect to the Earth bound coordinate system instead of using projections of helicopter velocity with respect to the moveable coordinate system as the output characteristics. Projecting the helicopter velocity onto an Earth bound coordinate system and then integrating velocity projections by time with initial conditions may solve this problem. This model has been used for the calculations of the Mi-8 helicopter with the new composite main rotor blades (designed at Belgrade Faculty of Mechanical Engineering), also with the new airfoils optimized for high subsonic speeds at the blade tips.

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